disabling login every 1800 seconds on phpmyadmin

On Ubuntu, phpmyadmin defaults to requiring you to login after 1800 seconds of inactivity. This is VERY annoying for me, because I only need phpmyadmin about once every 30 minutes or so, so I have to login each and every time I want to use it.

I googled and found a solution that says to add this line to /etc/phpmyadmin/config.inc.php

Code:

$cfg['LoginCookieValidity'] = 547847;

Well, I did that, but it still makes me log in every 30 minutes. Is there a more ubuntu-specific fixed needed?